In commercial and transactional printers, it is common to estimate ink usage to determine one of the major components of the cost to print a job with an ink jet printer. Conventional ink estimation methods involve having to first perform a rasterization (or raster image processing [RIP]) of the print job to produce a digital approximation to a continuous tone (“contone”) image. Subsequently, the contone image is halftoned with the same halftone producing algorithms and settings to be employed by a targeted printer, resulting in a halftoned digital image (or bitmap) that describes the drop (or dot) size for each pixel. The halftoned bitmap encodes the different drop sizes using a unique symbol for each drop size (e.g., level zero for no drop, one for small, two for medium, and three for large).
In an actual ink jet printer this halftoned bitmap data would be the input to the drivers of ink jet printheads. Hence the data used in an actual printer is the same as the data used to estimate ink usage for a print job. Since the drop sizes for an ink jet are known, the amount of ink required to print the job for each color may be calculated from a tally of the various drop symbols on each page as the sum of ink for each drop size, page and color.
However, the above-described ink estimation process is computationally intensive, since it involves rasterization, followed by halftoning, followed by counting the ink drops by size. Methods to speed up the process involve estimating the ink for a down-sampled image and multiplying the result by the down-sampling factor. For example, down-sampling the contone image data by a factor of two in both directions results in a bitmap having one quarter of the pixels of the original. An estimate using the sum of the ink drops, based on the downsampled image must be scaled by a factor of four to obtain an estimate for the ink usage of the original contone image. Yet this process is of limited utility, since the down sampling factor can only be made so large (e.g., normally 2 or 4 depending on rasterization resolution) before the bitmap resolution/quality is so low/degraded that the estimate becomes too inaccurate.
Even with down-sampling, the fact that the halftoned bitmap is used for ink estimation means that both the original image and the halftoned image must be recomputed to obtain a new estimate, if any parameter is changed. This is a process which touches every pixel at least twice.
Printer users frequently desire to know the effect of changing various printer settings on the cost of printing a large job. Accordingly, an improved mechanism to perform ink estimation is desired.